Optical parts are often fabricated by machining a substrate such as aluminum, including machining an optical surface on the substrate. These types of optical parts may, for example, be used as precision mirrors for long-range telescopes, multi-band imagers, military or commercial surveillance systems, targeting systems, laser designator systems, or other types of systems.
The performance and thus value of many optical systems is often limited in whole or in part by the accuracy and roughness of the optical surface on such an optical part. Existing techniques produce, at best, an optical surface with an RMS roughness of approximately 30 Angstroms. One effect of this degree of surface roughness is that, while existing systems may be used in the infrared (IR) range and, more recently, in the visible range, they are typically not suitable for use in the ultraviolet (UV) range. Also, some approaches require overcoat layers of significant thickness, but this can cause bi-material deformation in response to thermal changes. Accordingly, while existing techniques for fabricating optical surfaces have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.